High Q and low stress capacitor electrode array

ABSTRACT

An embodiment of the present invention provides a capacitor, including a solid electrode, an electrode broken into subsections with a signal bus lines connecting the subsections; and wherein the signal bus further connects the solid electrode with the electrode broken into subsections.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of priority under 35 U.S.C Section119 from U.S. Provisional Application Ser. No. 60/736,366, filed Nov.14, 2005, entitled, HIGH Q AND LOW STRESS CAPACITOR ELECTRODE ARRAY, byJames Martin.

BACKGROUND OF THE INVENTION

One of the most important parameters in evaluating a high frequency chipcapacitor is the Q factor, or the related equivalent series resistance(ESR). In theory, a “perfect” capacitor would exhibit an ESR of 0 (zero)ohms and would be purely reactive with no real (resistive) component.The current going through the capacitor would lead the voltage acrossthe capacitor by exactly 90 degrees at all frequencies.

In real world usage, no capacitor is perfect, and will always exhibitsome finite amount of ESR. The ESR varies with frequency for a givencapacitor, and is “equivalent” because its source is from thecharacteristics of the conducting electrode structures and in theinsulating dielectric structure. For the purpose of modeling, the ESR isrepresented as a single series parasitic element. In past decades, allcapacitor parameters were measured at a standard of 1 MHz, but intoday's high frequency world, this is far from sufficient. Typicalvalues for a good high frequency capacitor of a given value could run inthe order of about 0.05 ohms at 200 MHz, 0.11 ohms at 900 MHz, and 0.14ohms at 2000 MHz.

The quality factor Q, is a dimensionless number that is equal to thecapacitor's reactance divided by the capacitor's parasitic resistance(ESR). The value of Q changes greatly with frequency as both reactanceand resistance change with frequency. The reactance of a capacitorchanges tremendously with frequency or with the capacitance value, andtherefore the Q value could vary by a great amount.

Since a high capacitor Q is vital to many applications, a strongindustry need exists for the high Q and low stress capacitor electrodearray of the present invention.

SUMMARY OF THE INVENTION

An embodiment of the present invention provides a capacitor, comprisinga solid electrode, an electrode broken into subsections with a signalbus lines connecting the subsections; and wherein the signal bus furtherconnects the solid electrode with the electrode broken into subsections.The capacitor of an embodiment of the present invention may furthercomprise a voltage tunable dielectric material between the solidelectrode and the electrode broken into subsections to enable thecapacitor to be voltage tunable. The broken electrode may distribute thesignal across the capacitor area and increase the effective width of asignal path through the solid electrode. In an embodiment of the presentinvention and not limited in this respect, the capacitor may be a planarintegrated capacitors or a discrete ceramic capacitor and the capacitormay be a pair of series capacitors and wherein the subsections arearranged in such a manner that it increases the effective width of thesignal path in the solid electrode.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is described with reference to the accompanyingdrawings. In the drawings, like reference numbers indicate identical orfunctionally similar elements. Additionally, the left-most digit(s) of areference number identifies the drawing in which the reference numberfirst appears.

FIG. 1 illustrates three, of many possible, capacitor electrodestructures of some embodiments of the present invention; and

FIG. 2 illustrates a method of one embodiment of the present invention.

DETAILED DESCRIPTION

In the following detailed description, numerous specific details are setforth in order to provide a thorough understanding of the invention.However, it will be understood by those skilled in the art that thepresent invention may be practiced without these specific details. Inother instances, well-known methods, procedures, components and circuitshave not been described in detail so as not to obscure the presentinvention.

Use of the terms “coupled” and “connected”, along with theirderivatives, may be used. It should be understood that these terms arenot intended as synonyms for each other. Rather, in particularembodiments, “connected” may be used to indicate that two or moreelements are in direct physical or electrical contact with each other.“Coupled” my be used to indicated that two or more elements are ineither direct or indirect (with other intervening elements between them)physical or electrical contact with each other, and/or that the two ormore elements co-operate or interact with each other (e.g. as in a causean effect relationship).

An embodiment of the present invention provides a capacitor electrodestructure that allows for the creation of very high “Q” (low resistance)capacitors. It is particularly well suited to common capacitor materialstructures wherein one electrode is made from a higher resistance metalthan the opposite electrode. Examples of capacitors with such materialproperties can be found in planar integrated capacitors, as well asdiscrete ceramic capacitors. The structure of an embodiment of thepresent invention also reduces the mechanical stresses generated in themetals and dielectric films of the capacitor. The invention includeselectrodes broken into subsections, signal bus lines to connect thesubsections, and a solid electrode. The broken electrode should have thelower resistance of the two. The broken electrode may distribute thesignal across the capacitor area and, through proper arrangement,increase the effective width of the signal path through the higherresistance solid electrode. The signal busses may bring in and take outthe signal. Looking now at FIG. 1, in an embodiment of the presentinvention, the present electrodes may include a voltage tunabledielectric material 137 between the electrodes and the voltage tunabledielectric material may be a Parascan® voltage tunable dielectricmaterial.

This structure realizes these benefits by breaking two of the electrodesof a pair of series capacitors into subsections. The sections arearranged in such a manner that it increases the effective width of thesignal path in the higher resistance electrode. These subsections arethen electrically connected through signal bus line. The reduction instress occurs because the individual electrode subsections retain andcreate less stress than a single plate of similar area.

Continuing with FIG. 1, shown generally as 100 are images of two seriescapacitors. The left most, FIG. 1A, design 110 is fairly standard withsolid high resistance electrode 120 and low resistance electrodes 122connected by signal bus lines 115. Although not limited in this respect,two exemplary embodiments of the present invention are shown in thecenter 125 and on the right 140. Center capacitor, FIG. 1B 125, mayinclude solid high resistance electrode 135 and low resistanceelectrodes 132 connected by bus 130. Right capacitor, FIG. 1C 140, mayinclude solid high resistance electrode 150 and low resistanceelectrodes 155 connected by signal bus lines 145. The reduction inresistance, leading to an increase in Q, occurs because the length ofthe signal path stays the same while the effective width increases. Forexample, breaking the electrode as shown in the middle image 125increases the width to 3.5 times that of the conventional capacitor. Therightmost “diamond” configuration 140 increases that width to 4.25 timesthat of the conventional.

Turning now to FIG. 2, generally at 200, is provided a method accordingto one embodiment of the present invention which may comprise breakingan electrode into subsections 205 with signal bus lines connecting saidsubsections 210 and a solid electrode 215 to improve Q. The method mayfurther comprise distributing the signal across said capacitor area bysaid broken electrode and thereby increasing the effective width of asignal path through said solid electrode. The capacitor may be a planarintegrated capacitor or a discrete ceramic capacitor in the method of anembodiment of the present invention. The method may still furthercomprise adapting said solid electrode and said broken electrode toreduce the mechanical stresses generated in the metals and dielectricfilms of said capacitor and as shown at 220 using said capacitor in apair of series capacitors and wherein said subsections are arranged insuch a manner that it increases the effective width of the signal pathin said solid electrode. In an embodiment of the present method the atleast one voltage tunable dielectric capacitor may be a series networkof voltage tunable dielectric capacitors which are all tuned using acommon tuning voltage.

Throughout the aforementioned description, BST may be used as a tunabledielectric material that may be used in a tunable dielectric capacitorof the present invention. However, the assignee of the presentinvention, Paratek Microwave, Inc. has developed and continues todevelop tunable dielectric materials that may be utilized in embodimentsof the present invention and thus the present invention is not limitedto using BST material. This family of tunable dielectric materials maybe referred to as Parascan®.

The term Parascan® as used herein is a trademarked term indicating atunable dielectric material developed by the assignee of the presentinvention. Parascan® tunable dielectric materials have been described inseveral patents. Barium strontium titanate (BaTiO3-SrTiO3), alsoreferred to as BSTO, is used for its high dielectric constant(200-6,000) and large change in dielectric constant with applied voltage(25-75 percent with a field of 2 Volts/micron). Tunable dielectricmaterials including barium strontium titanate are disclosed in U.S. Pat.No. 5,312,790 to Sengupta, et al. entitled “Ceramic FerroelectricMaterial”; U.S. Pat. No. 5,427,988 by Sengupta, et al. entitled “CeramicFerroelectric Composite Material-BSTO-MgO”; U.S. Pat. No. 5,486,491 toSengupta, et al. entitled “Ceramic Ferroelectric CompositeMaterial-BSTO-ZrO2”; U.S. Pat. No. 5,635,434 by Sengupta, et al.entitled “Ceramic Ferroelectric Composite Material-BSTO-Magnesium BasedCompound”; U.S. Pat. No. 5,830,591 by Sengupta, et al. entitled“Multilayered Ferroelectric Composite Waveguides”; U.S. Pat. No.5,846,893 by Sengupta, et al. entitled “Thin Film FerroelectricComposites and Method of Making”; U.S. Pat. No. 5,766,697 by Sengupta,et al. entitled “Method of Making Thin Film Composites”; U.S. Pat. No.5,693,429 by Sengupta, et al. entitled “Electronically Graded MultilayerFerroelectric Composites”; U.S. Pat. No. 5,635,433 by Sengupta entitled“Ceramic Ferroelectric Composite Material BSTO-ZnO”; U.S. Pat. No.6,074,971 by Chiu et al. entitled “Ceramic Ferroelectric CompositeMaterials with Enhanced Electronic Properties BSTO Mg BasedCompound-Rare Earth Oxide”. These patents are incorporated herein byreference. The materials shown in these patents, especially BSTO-MgOcomposites, show low dielectric loss and high tunability. Tunability isdefined as the fractional change in the dielectric constant with appliedvoltage.

Barium strontium titanate of the formula Ba_(x)Sr_(1-x)TiO₃ is apreferred electronically tunable dielectric material due to itsfavorable tuning characteristics, low Curie temperatures and lowmicrowave loss properties. In the formula Ba_(x)Sr_(1-x)TiO₃, x can beany value from 0 to 1, preferably from about 0.15 to about 0.6. Morepreferably, x is from 0.3 to 0.6.

Other electronically tunable dielectric materials may be used partiallyor entirely in place of barium strontium titanate. An example isBa_(x)Ca_(1-x)TiO₃, where x is in a range from about 0.2 to about 0.8,preferably from about 0.4 to about 0.6. Additional electronicallytunable ferroelectrics include Pb_(x)Zr_(1-x)TiO₃ (PZT) where x rangesfrom about 0.0 to about 1.0, Pb_(x)Zr_(1-x)SrTiO₃ where x ranges fromabout 0.05 to about 0.4, KTa_(x)Nb_(1-x)O₃ where x ranges from about 0.0to about 1.0, lead lanthanum zirconium titanate (PLZT), PbTiO₃,BaCaZrTiO₃, NaNO₃, KNbO₃, LiNbO₃, LiTaO₃, PbNb₂O₆, PbTa₂O₆, KSr(NbO₃)and NaBa₂(NbO₃)5KH₂PO₄, and mixtures and compositions thereof. Also,these materials can be combined with low loss dielectric materials, suchas magnesium oxide (MgO), aluminum oxide (Al₂O₃), and zirconium oxide(ZrO₂), and/or with additional doping elements, such as manganese (MN),iron (Fe), and tungsten (W), or with other alkali earth metal oxides(i.e. calcium oxide, etc.), transition metal oxides, silicates,niobates, tantalates, aluminates, zirconnates, and titanates to furtherreduce the dielectric loss.

In addition, the following U.S. patents and patent Applications,assigned to the assignee of this application, disclose additionalexamples of tunable dielectric materials: U.S. Pat. No. 6,514,895,entitled “Electronically Tunable Ceramic Materials Including TunableDielectric and Metal Silicate Phases”; U.S. Pat. No. 6,774,077, entitled“Electronically Tunable, Low-Loss Ceramic Materials Including a TunableDielectric Phase and Multiple Metal Oxide Phases”; U.S. Pat. No.6,737,179 filed Jun. 15, 2001, entitled “Electronically TunableDielectric Composite Thick Films And Methods Of Making Same; U.S. Pat.No. 6,617,062 entitled “Strain-Relieved Tunable Dielectric Thin Films”;U.S. Pat. No. 6,905,989, filed May 31, 2002 entitled “Tunable DielectricCompositions Including Low Loss Glass”; U.S. patent application Ser. No.10/991,924, filed Nov. 18, 2004 entitled “Tunable Low Loss MaterialCompositions and Methods of Manufacture and Use Therefore” These patentsand patent applications are incorporated herein by reference.

The tunable dielectric materials can also be combined with one or morenon-tunable dielectric materials. The non-tunable phase(s) may includeMgO, MgAl₂O₄, MgTiO₃, Mg₂SiO₄, CaSiO₃, MgSrZrTiO₆, CaTiO₃, Al₂O₃, SiO₂and/or other metal silicates such as BaSiO₃ and SrSiO₃. The non-tunabledielectric phases may be any combination of the above, e.g., MgOcombined with MgTiO₃, MgO combined with MgSrZrTiO₆, MgO combined withMg₂SiO₄, MgO combined with Mg₂SiO₄, Mg₂SiO₄ combined with CaTiO₃ and thelike.

Additional minor additives in amounts of from about 0.1 to about 5weight percent can be added to the composites to additionally improvethe electronic properties of the films. These minor additives includeoxides such as zirconnates, tannates, rare earths, niobates andtantalates. For example, the minor additives may include CaZrO₃, BaZrO₃,SrZrO₃, BaSnO₃, CaSnO₃, MgSnO₃, Bi2O₃/2SnO₂, Nd₂O₃, Pr₇O₁₁, Yb₂O₃,H_(o2)O₃, La₂O₃, MgNb₂O₆, SrNb₂O₆, BaNb₂O₆, MgTa₂O₆, BaTa₂O₆ and Ta₂O₃.

Films of tunable dielectric composites may comprise Ba1-xSrxTiO3, wherex is from 0.3 to 0.7 in combination with at least one non-tunabledielectric phase selected from MgO, MgTiO₃, MgZrO₃, MgSrZrTiO₆, Mg₂SiO₄,CaSiO₃, MgAl₂O₄, CaTiO₃, Al₂O₃, SiO₂, BaSiO₃ and SrSiO₃. Thesecompositions can be BSTO and one of these components, or two or more ofthese components in quantities from 0.25 weight percent to 80 weightpercent with BSTO weight ratios of 99.75 weight percent to 20 weightpercent.

The electronically tunable materials may also include at least one metalsilicate phase. The metal silicates may include metals from Group 2A ofthe Periodic Table, i.e., Be, Mg, Ca, Sr, Ba and Ra, preferably Mg, Ca,Sr and Ba. Preferred metal silicates include Mg₂SiO₄, CaSiO₃, BaSiO₃ andSrSiO₃. In addition to Group 2A metals, the present metal silicates mayinclude metals from Group 1A, i.e., Li, Na, K, Rb, Cs and Fr, preferablyLi, Na and K. For example, such metal silicates may include sodiumsilicates such as Na₂SiO₃ and NaSiO₃—5H₂O, and lithium-containingsilicates such as LiAlSiO₄, Li2SiO₃ and Li₄SiO₄. Metals from Groups 3A,4A and some transition metals of the Periodic Table may also be suitableconstituents of the metal silicate phase. Additional metal silicates mayinclude Al₂Si₂O₇, ZrSiO₄, Ka1Si₃O₈, NaAlSi₃O₈, CaAl₂Si₂O₈, CaMgSi₂O₆,BaTiSi₃O₉ and Zn₂SiO₄. The above tunable materials can be tuned at roomtemperature by controlling an electric field that is applied across thematerials.

In addition to the electronically tunable dielectric phase, theelectronically tunable materials can include at least two additionalmetal oxide phases. The additional metal oxides may include metals fromGroup 2A of the Periodic Table, i.e., Mg, Ca, Sr, Ba, Be and Ra,preferably Mg, Ca, Sr and Ba. The additional metal oxides may alsoinclude metals from Group 1A, i.e., Li, Na, K, Rb, Cs and Fr, preferablyLi, Na and K. Metals from other Groups of the Periodic Table may also besuitable constituents of the metal oxide phases. For example, refractorymetals such as Ti, V, Cr, Mn, Zr, Nb, Mo, Hf, Ta and W may be used.Furthermore, metals such as Al, Si, Sn, Pb and Bi may be used. Inaddition, the metal oxide phases may comprise rare earth metals such asSc, Y, La, Ce, Pr, Nd and the like.

The additional metal oxides may include, for example, zirconnates,silicates, titanates, aluminates, stannates, niobates, tantalates andrare earth oxides. Preferred additional metal oxides include Mg₂SiO₄,MgO, CaTiO₃, MgZrSrTiO₆, MgTiO₃, MgA₁₂O₄, WO3, SnTiO₄, ZrTiO₄, CaSiO₃,CaSnO₃, CaWO₄, CaZrO₃, MgTa₂O₆, MgZrO₃, MnO₂, PbO, Bi₂O₃ and LaO₃.Particularly preferred additional metal oxides include Mg₂SiO₄, MgO,CaTiO₃, MgZrSrTiO₆, MgTiO₃, MgAl₂O₄, MgTa₂O₆ and MgZrO₃.

The additional metal oxide phases are typically present in total amountsof from about 1 to about 80 weight percent of the material, preferablyfrom about 3 to about 65 weight percent, and more preferably from about5 to about 60 weight percent. In one preferred embodiment, theadditional metal oxides comprise from about 10 to about 50 total weightpercent of the material. The individual amount of each additional metaloxide may be adjusted to provide the desired properties. Where twoadditional metal oxides are used, their weight ratios may vary, forexample, from about 1:100 to about 100:1, typically from about 1:10 toabout 10:1 or from about 1:5 to about 5:1. Although metal oxides intotal amounts of from 1 to 80 weight percent are typically used, smalleradditive amounts of from 0.01 to 1 weight percent may be used for someapplications.

The additional metal oxide phases can include at least two Mg-containingcompounds. In addition to the multiple Mg-containing compounds, thematerial may optionally include Mg-free compounds, for example, oxidesof metals selected from Si, Ca, Zr, Ti, Al and/or rare earths.

While the present invention has been described in terms of what are atpresent believed to be its preferred embodiments, those skilled in theart will recognize that various modifications to the discloseembodiments can be made without departing from the scope of theinvention as defined by the following claims.

1. An apparatus, comprising: a capacitor including a solid electrode;and an electrode broken into subsections with signal bus linesconnecting said subsections such that the length of a signal path staysthe same while an effective width increases thereby creating a reductionin resistance, leading to an increase in Q; wherein said brokenelectrode is constructed of a lower resistance metal than said solidelectrode and wherein a voltage tunable dielectric material is betweensaid electrodes; and wherein the voltage tunable dielectric material isa series network of voltage tunable dielectric capacitors which are alltuned using a common tuning voltage.
 2. The apparatus of claim 1,wherein said solid electrode and said broken electrode are adapted toreduce the mechanical stresses generated in metals and dielectric filmsof said capacitor.
 3. The apparatus of claim 1, wherein said subsectionsform a diamond shape.
 4. The apparatus of claim 1, wherein saidsubsections form a plurality of adjacent rectangular shapes.
 5. Acapacitor, comprising: a solid electrode; an electrode broken intosubsections with signal bus lines connecting said subsections such thatthe length of a signal path stays the same while an effective widthincreases thereby creating a reduction in resistance, leading to anincrease in Q; wherein said broken electrode is constructed of a lowerresistance metal than said solid electrode and wherein a voltage tunabledielectric material is between said electrodes; said capacitor is in apair of series capacitors and wherein said subsections are arranged insuch a manner that it increases the effective width of the signal pathin said solid electrode; and wherein said pair of series capacitors is aseries network of voltage tunable dielectric capacitors which are alltuned using a common tuning voltage.
 6. The capacitor of claim 5,wherein said broken electrode distributes the signal across an area ofsaid capacitor and increases the effective width of a signal paththrough said solid electrode.
 7. A capacitor, comprising: a firstelectrode; a second electrode comprising a plurality of subsectionsconnected via signal bus lines, wherein a change of dimensions of asignal path over a length of the signal path creates a reduction inresistance and an increase in Q, wherein the second electrode comprisesa lower resistance metal than the first electrode and wherein a voltagetunable dielectric material is between the first and second electrodes;wherein said capacitor is in a pair of series capacitors and whereinsaid subsections are arranged in such a manner that it increases theeffective width of the signal path in said first electrode; and whereinsaid pair of series capacitors is a series network of voltage tunabledielectric capacitors which are all tuned using a common tuning voltage.8. The capacitor of claim 7, wherein said subsections form a diamondshape.
 9. The capacitor of claim 7, wherein said subsections form aplurality of adjacent rectangular shapes.
 10. The capacitor of claim 7,wherein the first electrode is adapted to reduce the mechanical stressesgenerated in metals and dielectric films of the capacitor.
 11. Thecapacitor of claim 7, wherein the second electrode is adapted to reducethe mechanical stresses generated in metals and dielectric films of thecapacitor.